Ftp data transmission in stack system

ABSTRACT

According to an example, a file transfer protocol data transmission method applied in a stack system includes an FTP server master process receiving a file transfer request from an FTP client, for a file requested by the file transfer request, the FTP server master process judging whether the file and the FTP server master process are in a same chassis, when the file and the FTP server master process are not in the same chassis, the FTP server master process sends a file transfer notice to an FTP server slave process running on a chassis which is in the stack system and which the file is in.

BACKGROUND

File Transfer Protocol (FTP) is a universal protocol used to transferfiles between an FTP server and an FTP client, and is described indetail in RFC 959. FTP can be applied in a stack system. The stacksystem refers to a system consisting of multiple chassis devices (called“chassis” for short). In the stack system, one chassis is selected as amaster chassis according to a preset selection principle, and the otherchassis are regarded as slave chassis. An FTP server master process runson the master chassis, and an FTP server slave process runs on one ofthe slave chassis.

BRIEF DESCRIPTION OF THE DRAWINGS

Features of the present disclosure are illustrated by way of example andnot limited in the following figure(s), in which like numerals indicatelike elements, in which:

FIG. 1 is a network diagram illustrating an FTP applied to a stacksystem.

FIG. 2 is a flow chart of a method provided in one example of thepresent disclosure.

FIG. 3 is a detailed flow chart of a method provided in one example ofthe present disclosure.

FIG. 4 is a schematic diagram illustrating a socket format provided inone example of the present disclosure.

FIG. 5 is a flow chart of an example of the present disclosure.

FIG. 6 is a schematic diagram illustrating an apparatus provided in oneexample of the present disclosure.

DETAILED DESCRIPTION

For simplicity and illustrative purposes, the present disclosure isdescribed by referring mainly to examples thereof. In the followingdescription, numerous specific details are set forth in order to providea thorough understanding of the present disclosure. It will be readilyapparent however, that the present disclosure may be practiced withoutlimitation to these specific details. In other instances, some methodsand structures have not been described in detail so as not tounnecessarily obscure the present disclosure. Throughout the presentdisclosure, the terms “a” and “an” are intended to denote at least oneof a particular element. As used herein, the term “includes” meansincludes but not limited to, the term “including” means including butnot limited to. The term “based on” means based at least in part on.

FIG. 1 is a network diagram illustrating an FTP applied to a stacksystem. Referring to FIG. 1, a PC A, as an FTP client, is connected to aslave chassis in a stack system; an FTP server master process runs on amaster chassis, and an FTP server slave process runs on the slavechassis. Under normal circumstances, the FTP server master process is inworking condition, while the FTP server slave process, as a backup ofthe FTP server master process, is in a standby state.

As shown in FIG. 1, if the PC A tries to acquire a file xxx.log storedin the slave chassis, the PC A first sends a file download request tothe FTP server master process. When the FTP server master processreceives the file download request sent by the PC A, the FTP servermaster process finds that the file requested by the PC A is in the slavechassis. Since the FTP server slave process in the slave chassis is inthe standby state and does not work, the FTP server master processacquires the file xxx.log from the slave chassis through a stack link,such as an Intelligent Resilient Framework (IRF) link between the masterchassis and the slave chassis. The FTP server master process transmitsthe acquired file xxx.log back to the slave chassis through the stacklink, such as the IRF link between the master chassis and the slavechassis, and the slave chassis then forwards the acquired file xxx.logto the PC A.

It can be seen from the above described procedure that the PC A acquiresthe file xxx.log, the stack link between the master chassis and theslave chassis is frequently occupied in the procedure. For example, theFTP server master process acquires the file xxx.log from the slavechassis through the stack link, such as the IRF link between the masterchassis and the slave chassis, and transmits the acquired file xxx.logback to the slave chassis through the stack link, such as the IRF linkbetween the master chassis and the slave chassis. This causes anincrease of interactive packets on the stack link between the masterchassis and the slave chassis, which increases packet pressure on thestack link and results in an increased risk of stack split.

Embodiments of the present disclosure will be explained hereinafter indetail with reference to the accompanying drawings as well as examples.

Two kinds of links will be established when a file is transmittedbetween an FTP server and an FTP client: one is a control link fortransmission of FTP control information, and the other is a data linkfor transmission of files. Based on an initiator of a data connection,the data link can be established in one of an active mode and a passivemode. The active mode means that the FTP server actively initiates adata connection when establishing a data link, while the passive modemeans that the FTP client actively initiates a data connection whenestablishing a data link.

A method for transmitting FTP data applied in a stack system provided inone example of the present disclosure is to modify establishment of adata link in the case of a file transfer request, and makes no changesin the control link and establishment of data links in other cases. Theestablishment of the data link can use the active mode, and can also usethe passive mode, and this is not specifically limited in one example ofthe present disclosure.

Besides, in one example of the present disclosure, the file transferrequest can be a file download request or a file upload request. Thefile download request here can be a single file/batch file downloadrequest, and the file upload request here can be a single file/batchfile upload request.

The method provided in one example of the present disclosure will bedescribed in below.

FIG. 2 is a flow chart of a method provided in one example of thepresent disclosure. The flow can be applied to a stack system. Referringto FIG. 2, the flow can include following blocks:

Block 201: receiving, by an FTP server master process in the stacksystem, a file transfer request from an FTP client.

The file transfer request can be a file download request or a fileupload request.

Block 202: for each file of the file transfer request, judging, by theFTP server master process, whether the file and the FTP server masterprocess are in a same chassis. If the file and the FTP server masterprocess are not in a same chassis, performing block 203.

If a judgment result of the block 202 is yes, it shows that the file andthe FTP server master process are in a same chassis, and the FTP servermaster process can directly perform transmission of the file. Forexample, the FTP server master process can directly perform thetransmission of the file according to an existing manner of performingtransmission of files by an FTP server master process.

If the judgment result of the block 202 is not, it shows that the fileand the FTP server master process are not in a same chassis. Forexample, the file is in a slave chassis of the stack system while theFTP server master process is in the master chassis of the stack system.If the file is transmitted according to the existing file transmissionmanner, it will result in the stack link between the master chassis andthe slave chassis being frequently occupied to transmit file, therebyincreasing packet pressure on the stack link. In order to avoid thisproblem, the block 203 is performed in one example of the presentdisclosure.

Block 203: sending, by the FTP server master process, a file transfernotice to an FTP server slave process running on a chassis which is inthe stack system and which the file is in, and taking over, by this FTPserver slave process, execution of transmission of the file through adata link for transferring the file between this FTP server slaveprocess and the FTP server client after this FTP server slave processreceives the file transfer notice.

That is to say, in one example of the present disclosure, when the fileto be transferred and the FTP server master process are not in the samechassis, the transmission of the file will not be executed by the FTPserver master process. Instead of the FTP server master process, thetransmission of the file will be executed by the FTP server slaveprocess in the chassis that has the file. Compared this with theexisting file transfer manner, the problem that the stack link betweenthe slave chassis and the master chassis being frequently occupied totransmit files will not appear, and the pressure on the stack link willbe reduced.

The flow shown in FIG. 2 will be described in details by taking a filedownload request as an example of the file transfer request. Theprinciple of a file upload request is similar.

FIG. 3 is a detailed flow chart of a method provided in one example ofthe present disclosure. The flow can be applied in the network shown inFIG. 1. As shown in FIG. 3, the flow can include following blocks.

Block 301: when starting a new FTP connection, randomly assigning atransmission control protocol (TCP) port, by a PC A as an FTP client, tothe FTP client, and sending a connection request to an FTP server masterprocess through the TCP port.

Block 302: after the FTP server master process running in a masterchassis receives the connection request, establishing, by the FTP servermaster process, a control link with the PC A through athree-way-handshake.

Block 303: sending, by the PC A, a logged in user name and password of acorresponding user of the PC A through the control link between the PC Aand the FTP server master process to the FTP server master process forauthentication.

After the logged in user name and password sent by the PC A passauthentication, it shows that the corresponding user of the PC A hassuccessfully logged in the FTP server master process. Accordingly, theuser can be called a “logged in user.”

The above blocks 301 to 303 are preparation work of the PC A and the FTPserver master process before the file download request is sent. Thepreparation work can also include other blocks which will not bedescribed here since they have little relation with the example of thepresent disclosure.

Block 304: sending, by the PC A, a file download request from the loggedin user to the FTP server master process. The file download requestcarries a port identifier of the PC A for data link and file identifiersof files which the PC A is to download.

Block 305: determining for each file identifier in the file downloadrequest, by the FTP server master process, a chassis that has a file(recorded as file 1) corresponding to the file identifier by parsing aworking directory of the logged in user.

In the block 305, determining a chassis that has a file (recorded asfile 1) corresponding to the file identifier by parsing a workingdirectory of the logged in user can include: judging whether the fileidentifier carries a chassis identifier of a chassis that has the filecorresponding to the file identifier; if yes, directly determining achassis corresponding to the carried chassis identifier as the chassisthat has the file (recorded as file 1) corresponding to the fileidentifier and then performing following block 306; otherwise,determining a chassis that has a file (recorded as file 1) correspondingto the file identifier by parsing a working directory of the logged inuser.

Furthermore, in one example of the present invention, the FTP servermaster process can use serial mode to handle requests from the FTPclient. That is, the FTP client sends a request and the FTP servermaster process handles or aborts the request before the FTP client cansend a next request. A request described here refers to an operationviewed from the user and it may not be a single command. A request maycorrespond to multiple commands and multiple responses. Taking a filerenaming request as an example, after the user has inputted a file namebefore modification and a modified file name in the FTP client, the FTPclient first sends a RENAME FROM (RNFR) command carrying the file nameto be modified, and then sends a RENAME TO (RNTO) command carrying themodified file name. The file renaming request is completed when the FTPserver master process has responded to both of the two commands.

Based on this, in the block 305, no matter if the file download requestis a single file download request or a batch file download request, thefile download request may carry multiple file identifiers. Based onthis, the FTP server master process will perform the determinationoperation of the block 305 for each file identifier carried in the filedownload request.

In addition, when the working directory of the logged in user is locatedin a chassis of the stack system, then each file identifier of the filedownload request corresponds to a file located on that chassis.

Block 306: judging, by the FTP server master process, whether thedetermined chassis is a chassis which the FTP server master process islocated; if yes, performing the file download according to an existingmanner; otherwise performing block 307.

Block 307: sending, by the FTP server master process, a file transfernotice to an FTP server slave process running on a chassis, which is inthe stack system and has the file 1, to instruct the FTP server slaveprocess to prepare to take over the download of the file 1.

The notice carries a port identifier of the PC A for data link and afile identifier of the file 1.

Block 308: after the FTP server slave process receives the file transfernotice, judging, by the FTP server slave process, whether there is adata link for transferring the file 1 existing between the FTP serverslave process and the FTP client; if not, performing block 309; if yes,performing block 311.

Block 309: opening, by the FTP server slave process, a local port 20 toestablish a data link with a port corresponding to the port identifierin the file transfer notice, where the date link is to transfer the file1 and return a response message for the file transfer notice to the FTPserver master process.

In the block 309, the response message carries the port identifier ofthe PC A for data link and the file identifier of the file 1.

It can be seen, after executing the block 309, a data link isestablished to transfer the file 1 between the local port 20 of the FTPserver slave process and the port of the PC A corresponding to the portidentifier in the file transfer notice.

It should be noted that, in the block 309, using the active mode toestablish a data link is taken as an example, and the principle of usingthe passive mode to establish a data link is similar and will not berepeated here.

Block 310: after the FTP server master process receives the responsemessage of the FTP server slave process, notifying, by the FTP servermaster process through the control link between the FTP server masterprocess and the PC A, the PC A that a data link for transferring thefile 1 has been established, and notifying the FTP server slave processto start transmission of the file 1 through the data link fortransferring the file 1. Then, block 311 is performed.

Block 311: transmitting, by the FTP server slave process, the file 1 tothe PC A through the data link for transferring the file 1.

Block 312: after the transmission of the file 1 is completed, closing,by the FTP server slave process, the data link established between theFTP server slave process and the PC A to transfer the file 1, andsending a file transfer completion notice to the FTP server masterprocess to notify the FTP server master process that the transmission ofthe file 1 is completed.

Block 313: after the FTP server master process receives the filetransfer completion notice, notifying, by the FTP server master processthrough the control link between the FTP server master process and thePC A, the FTP client that the transmission of the file has beentransferred.

It should be noted, in one example of the present disclosure, in thefile transmission procedure of the block 311, the FTP server masterprocess is in a dormant state. When the file transfer completion noticeis received, the FTP server master process is wakened again.

With this, the download of the file can be completed through the aboveblocks.

It should be noted, in the flow shown in FIG. 3, each of the noticessent by the FTP server master process to the FTP server slave process,and the response messages and each of the notices sent by the FTP serverslave process to the FTP server master process, are sent via a socketsuch as an interprocess Socket. The format of the Socket is shown inFIG. 4 and includes: FLAG field, type field, file identifier field, andport identifier field of client for data link.

The FLAG field occupies one byte, and meanings of values of the FLAGfield can be: when a value of bit0 is 1, i.e., a value of the FLAG fieldis 1, it means that the FTP server slave process notifies the FTP servermaster process of file transmission completion (referred to as “fin”);when a value of bit1 is 1, i.e., a value of the FLAG field is 2, itmeans that the FTP server master process notifies the FTP server slaveprocess to prepare to take over file transmission (referred to as“syn”); when a value of bit2 is 1, i.e., a value of the FLAG field is 4,it means that the FTP server slave process has responded to the FTPserver master process; other bits such as from bit3 to bit7 can bereserved. The type field occupies one byte, and meanings of values ofthe type field can be: when a value of type field is 1, it means that adata link is established; when a value of type field is 0, it means thatthe data link is closed. The file identifier field occupies 255 bytes,and is to carry file identifiers and file paths. The port identifierfield of client for data link occupies 2 bytes.

Based on FIG. 4, the flow shown in FIG. 3 will be described hereinafterwith an example.

FIG. 5 is a flow chart of an example of the present disclosure. In FIG.5, the PC A, as an FTP Client, is directly connected with a slavechassis of a stack system, an FTP server master process runs on a masterchassis of the stack system, an FTP server slave process runs on a slavechassis, a PC A tries to download and acquire a file of which a fileidentifier is cmdtree.txt, and the file is stored in a main controlboard of the slave chassis. Based on this, as shown in FIG. 5, the flowcan include the following blocks.

Block 501: before the PC A (address is 192.168.10.1) initiates an FTPconnection, first randomly assigning, by the PC A, a transmissioncontrol protocol (TCP) port to the PC A itself, and sending a connectionrequest to an FTP port (default is 21) of the FTP server master process(address is 192.168.10.33) by using the TCP port.

Block 502: after the FTP server master process receives the connectionrequest, establishing, by the FTP server master process, a control linkwith the PC A.

Block 503: inputting, by the PC A, a logged in user name and passwordand sending the logged in user name and the password to the FTP servervia the control link for authentication.

Block 504: sending, by the PC A, a file download request from a loggedin user which has passed authentication to the FTP server masterprocess. The request carries a port identifier of the PC A for the datalink, such as 1215, and the file cmdtree.txt.

Block 505: acquiring, by the FTP server master process, a default workpath of a root directory of the logged in user, and parsing the workpath to determine that the file cmdtree.txt is located is the slavechassis with a chassis identifier of 2 and the FTP server master processis located is the master chassis with a chassis identifier of 1, therebyconcluding that the file cmdtree.txt and the FTP server master processare in different chassis.

The FTP server master process can obtain files only in the default workpath of the logged in user. If the default work path is a compact Flash(CF) card in the master chassis while the file is in the slave chassis,the FTP server master process first modifies the default work path to bea CF card in the slave chassis according to a working principle of localusers.

Block 506: sending, by the FTP server master process, a file transfernotice to an FTP server slave process on a slave chassis having a slaveidentifier of 2.

Based on FIG. 4, a format of the file transfer notice in the block 506is shown in Table 1.

TABLE 1 Port identifier field of FLAG field Type field File identifierfield client for data link 2 1 /cmdtree.txt 1215

Block 507: after the FTP server slave process receives the notice,checking, by the FTP server slave process, whether a data link isestablished between a local port 20 and a port 1215 of the PC A, i.e.,192.168.10.1-1215; if the data link between the local port 20 and theport 1215 of the PC A is not established, performing block 508; if thedata link between the local port 20 and the port 1215 of the PC A isestablished, performing block 510.

Block 508: opening, by the FTP server slave process, the local port 20,and establishing a data link between the local port 20 and the port 1215of the PC A, i.e., 192.168.10.1-1215; after the data link isestablished, returning a response message to the FTP server masterprocess to inform the FTP server master process that the data link isestablished.

Based on FIG. 4, a format of the response message in the block 508 isshown in Table 2.

TABLE 2 Type Port identifier field of FLAG field field File identifierfield client for data link 4 1 /cmdtree.txt 1215

Block 509: after the FTP server master process receives the aboveresponse message, informing, by the FTP server master process throughthe control link between the FTP server master process and the PC A, thePC A that the data link for transferring the file cmdtree.txt has beenestablished, and notifying the FTP server slave process to starttransmission of the file cmdtree.txt.

In the block 509, a format of the notice which is sent from the FTPserver master process to the FTP server slave process may be as shown inthe above Table 1.

Block 510: transferring, by the FTP server slave process through thedata link between the local port 20 and 192.168.10.1-1215, i.e., theport 1215 of the PC A, the file cmdtree.txt.

Block 511: after the transmission of the file cmdtree.txt is completed,closing, by the FTP server slave process, the data link for transferringthe file cmdtree.txt between the FTP server slave process and the PC A,i.e., the data link between the local port 20 and 192.168.10.1-1215, andsending a file transfer completion notice to the FTP server masterprocess.

Based on FIG. 4, a format of the file transfer completion notice in theblock 511 is shown in Table 3.

TABLE 3 Type Port identifier field of FLAG field field File identifierfield client for data link 1 1 /cmdtree.txt 1215

Block 512: after the FTP server master process receives the filetransfer completion notice, notifying, by the FTP server master processthrough the control link between the FTP server master process and theFTP client, the PC A of the file, that the transmission has beencompleted.

At this point, the description of the flow shown in FIG. 5 has beencompleted.

In the above flow shown in FIG. 3 or FIG. 5, after the FTP server slaveprocess has closed the data link, the FTP server slave process cannotify the FTP server master process through a notice which may use aformat shown in Table 4, that the data link has been closed.

TABLE 4 Type Port identifier field of FLAG field field File identifierfield client for data link 4 2 1215

Further, in the above flow shown in FIG. 3 or FIG. 5, the FTP serverslave process can close the data link established between the FTP serverslave process and the PC A to transfer the file 1, after waiting for aset time when the transmission of the file 1 is completed. The waitingset time can specifically be set according to the actual situation, forexample, can be immediate, or a certain time such as 1 minute, 30seconds and so on. An example of the present disclosure does notparticularly limit this, or the set time can also be a time when a linkclosing notice sent by the FTP server master process is received. TheFTP server master process can send the link closing notice in followingsituations: the FTP server master process is wakened again by receivingthe file transfer completion notice and determines whether filescorresponding to all the file identifiers in the file download requesthave been downloaded. If the files corresponding to all the fileidentifiers in the file download request have been downloaded, the FTPserver master process sends the link closing notice to the FTP serverslave process in a chassis, in which a file corresponding to each fileidentifier of the file download request is located, to inform the FTPserver slave process to close the data link for transferring the filecorresponding to the file identifier of the file download requestbetween the FTP server slave process and the PC A. If the FTP servermaster process determines that files corresponding to some of the fileidentifiers in the file download request have not been downloaded, forthe file identifiers corresponding to the files which have not beendownloaded, the above operation of determining a chassis in which a filecorresponding to the file identifier is located is repeated.

The method provided in one example of the present disclosure has beendescribed above; an apparatus provided in one example of the presentdisclosure will be described hereinafter.

Referring to FIG. 6, FIG. 6 is a schematic diagram illustrating anapparatus provided in one example of the present disclosure. As shown inFIG. 6, the apparatus can include: a master chassis and a slave chassis,an FTP server master process runs on the master chassis, and an FTPserver slave process runs on the slave chassis.

The FTP server master process includes a request receiving unit, ajudgment unit and a transfer notification unit.

The request receiving unit is to receive a file transfer request from anFTP client.

The judgment unit is to, for a file requested by the file transferrequest, judge whether the file and the FTP server master process are ina same chassis.

The transfer notification unit is to, when a judgment result of thetransfer notification unit is no, send a file transfer notice to an FTPserver slave process running on a chassis in the stack system and thathas the file.

The FTP server slave process includes a notification receiving unit anda transfer unit.

The notification receiving unit is to receive the file transfer noticefrom the FTP server master process.

The transfer unit is to, after the notification receiving unit receivesthe file transfer notice, take over execution of transmission of thefile through a data link for transferring the file between this FTPserver slave process and the FTP client.

When execution of the file transmission, the transfer unit can includefollowing sub-units:

a judgment sub-unit to judge whether there is a data link fortransferring the file existing between the FTP server slave process andthe FTP client;

an establishment sub-unit to establish a data link for transferring thefile between the FTP server slave process and the FTP client when ajudgment result of the judgment sub-unit is no;

a transfer sub-unit to transmit the file through the data link fortransferring the file, when a judgment result of the judgment sub-unitis yes or when the establishment sub-unit has established the data linkfor transferring the file.

In one example of the present disclosure, the FTP server slave processfurther includes a link notification unit.

The link notification unit is to send a data link establishmentcompletion notice to the FTP server master process, after theestablishment sub-unit has established the data link before the transfersub-unit transmits of the file through the data link established by theestablishment sub-unit.

Based on this, the request receiving unit of the FTP server masterprocess further receives the data link establishment completion notice;the transfer notification unit further notifies the FTP client through acontrol link between the FTP server master process and the FTP clientthat the data link has been established, after the request receivingunit receives the data link establishment completion notice. Thetransfer notification unit notifies the transfer sub-unit to starttransmission of the file through the data link established by theestablishment sub-unit after completing notification of the FTP clientthat the data link has been established.

Further, in one example of the present disclosure, the FTP server slaveprocess further includes:

a link manage unit to, after the transfer sub-unit completes the filetransmission, close the data link for transferring the file between theFTP server slave process and the FTP client, and send a file transfercompletion notice to the FTP server master process.

Based on this, the request receiving unit of the FTP server masterprocess further receives the file transfer completion notice. After therequest receiving unit receives the file transfer completion notice, thetransfer notification unit further notifies the FTP client of the fileswhich have been completely downloaded, through the control link betweenthe transfer notification unit and the FTP client.

In one example of the present disclosure, the notices sent by the FTPserver master process to the FTP server slave process and the noticessent by the FTP server slave process to the FTP server master processcan be sent via sockets.

In examples of the present disclosure, when the file to be transferredand the FTP server master process are not in the same chassis, thetransmission of the file will not be executed by the FTP server masterprocess, and the transmission of the file will be executed by the FTPserver slave process in the chassis in which the file is located,instead of the FTP server master process. Compared this with theexisting file transfer manner, the problem that the stack link betweenthe slave chassis and the master chassis is frequently occupied totransmit files will not appear, and the pressure on the stack link willbe reduced.

The methods, units and apparatus described herein may be implemented byhardware, machine-readable instructions or a combination of hardware andmachine-readable instructions. Machine-readable instructions used in theexamples disclosed herein may be stored in storage medium readable bymultiple processors, such as hard drive, CD-ROM, DVD, compact disk,floppy disk, magnetic tape drive, RAM, ROM or other proper storagedevice. Or, at least part of the machine-readable instructions may besubstituted by specific-purpose hardware, such as custom integratedcircuits, gate array, FPGA, PLD and specific-purpose computers and soon.

A machine-readable storage medium is also provided, which is to storeinstructions to cause a machine to execute a method as described herein.Specifically, a system or apparatus having a storage medium that storesmachine-readable program codes for implementing functions of any of theabove examples and that may make the system or the apparatus (or CPU orMPU) read and execute the program codes stored in the storage medium.

In this situation, the program codes read from the storage medium mayimplement any one of the above examples, thus the program codes and thestorage medium storing the program codes are part of the technicalscheme.

The storage medium for providing the program codes may include floppydisk, hard drive, magneto-optical disk, compact disk (such as CD-ROM,CD-R, CD-RW, DVD-ROM, DVD-RAM, DVD-RW, DVD+RW), magnetic tape drive,Flash card, ROM and so on. Optionally, the program code may bedownloaded from a server computer via a communication network.

It should be noted that, alternatively to the program codes beingexecuted by a computer, at least part of the operations performed by theprogram codes may be implemented by an operation system running in acomputer following instructions based on the program codes to realize atechnical scheme of any of the above examples.

In addition, the program codes implemented from a storage medium arewritten in a storage in an extension board inserted in the computer orin a storage in an extension unit connected to the computer. In thisexample, a CPU in the extension board or the extension unit executes atleast part of the operations according to the instructions based on theprogram codes to realize a technical scheme of any of the aboveexamples.

Although described specifically throughout the entirety of the instantdisclosure, representative examples of the present disclosure haveutility over a wide range of applications, and the above discussion isnot intended and should not be construed to be limiting, but is offeredas an illustrative discussion of aspects of the disclosure.

What has been described and illustrated herein are examples along withsome of its variations. The terms, descriptions and figures used hereinare set forth by way of illustration only and are not meant aslimitations. Many variations are possible within the spirit and scope ofthe subject matter, which is intended to be defined by the followingclaims—and their equivalents—in which all terms are meant in theirbroadest reasonable sense unless otherwise indicated.

What is claimed is:
 1. A file transfer protocol (FTP) data transmissionmethod applied in a stack system, the method comprising: receiving, byan FTP server master process in the stack system, a file transferrequest from an FTP client; and for a file requested by the filetransfer request, judging, by the FTP server master process, whether thefile and the FTP server master process are in a same chassis; if thefile and the FTP server master process are not in the same chassis:sending, by the FTP server master process, a file transfer notice to anFTP server slave process running on a chassis which is in the stacksystem and which the file is in.
 2. The method of claim 1, wherein themethod further comprises: after the FTP server master process receives adata link establishment completion notice from the FTP server slaveprocess, notifying, by the FTP server master process, the FTP clientthrough a control link between the FTP server master process and the FTPclient that the data link has been established; after notifying the FTPclient that the data link has been established, notifying, by the FTPserver master process, the FTP server slave process to start thetransmission of the file through the data link.
 3. The method of claim2, wherein the method further comprises: after the FTP server masterprocess receives a file transfer completion notice from the FTP serverslave process, notifying, by the FTP server master process, the FTPclient that the file has been completely transferred, through a controllink between the FTP server master process and the FTP client.
 4. Themethod of claim 2, wherein notices sent by the FTP server master processto the FTP server slave process and notices sent by the FTP server slaveprocess to the FTP server master process are sent via sockets.
 5. Themethod of claim 1, wherein when the file and the FTP server masterprocess are in the same chassis, the FTP server master process directlyperforms the transmission of the file.
 6. A file transfer protocol (FTP)data transmission method applied in a stack system, the methodcomprising: receiving, by an FTP server slave process in the stacksystem, a file transfer notice from an FTP server master process;wherein the file transfer notice instructs the FTP server slave processto take over download of a file which is requested by an FTP client andis in a chassis where the FTP server slave process runs; taking over, bythe FTP server slave process execution of transmission of the filethrough a data link to transfer the file between the FTP server slaveprocess and the FTP client after the FTP server slave process receivesthe file transfer notice.
 7. The method of claim 6, wherein the takingover, by the FTP server slave process execution of transmission of thefile through a data link to transfer the file between the FTP serverslave process and the FTP client after the FTP server slave processreceives the file transfer notice comprises: judging, by the FTP serverslave process, whether the data link to transfer the file exists betweenthe FTP server slave process and the FTP client; when the data link totransfer the file exists between the FTP server slave process and theFTP client, directly performing, by the FTP server slave process, thetransmission of the file through the existing data link; when the datalink to transfer the file does not exist between the FTP server slaveprocess and the FTP client, establishing, by the FPT server slaveprocess, the data link to transfer the file between the FTP server slaveprocess and the FTP client and performing the transmission of the filethrough the established data link.
 8. The method of claim 7, whereinafter the FTP server slave process has established the data link andbefore the FTP server slave process executes the transmission of thefile through the established data link, the method further comprises:sending, by the FTP server slave process, a data link establishmentcompletion notice to the FTP server master process.
 9. The method ofclaim 7, wherein the method further comprises: after FTP server slaveprocess completes the transmission of the file, closing, by the FTPserver slave process, the data link to transfer the file between the FTPserver slave process and the FTP client, and sending a file transfercompletion notice to the FTP server master process.
 10. A network devicecapable of acting as a master device in a stack system, the networkdevice comprising a request receiving unit, a judgment unit, and atransfer notification unit; wherein: the request receiving unit is toreceive a file transfer request from an FTP client; the judgment unit isto, for a file requested by the file transfer request, judge whether thefile is in the network device; the transfer notification unit is to,when a judgment result of the judgment notification unit is no, send afile transfer notice to an FTP server slave process running on a chassiswhich is in the stack system and which has the file.
 11. The networkdevice of claim 10, wherein the request receiving unit is further toreceive a data link establishment completion notice and a file transfercompletion notice from the FTP server slave process; the transfernotification unit is further to notify: the FTP client through a controllink between the network device and the FTP client that a data link hasbeen established to transfer the file between the FTP server slaveprocess and the FTP client after the request receiving unit receives thedata link establishment completion notice; the FTP server slave processto start transmission of the file through the data link established totransfer the file between the FTP server slave process and the FTPclient; and the FTP client through the control link between the transfernotification unit and the FTP client that the file has been completelytransferred, after the request receiving unit receives the file transfercompletion notice.
 12. A network device capable of acting as a slavedevice in a stack system, the network device comprising a notificationreceiving unit and a transfer unit; wherein the notification receivingunit is to receive a file transfer notice from an FTP server masterprocess; wherein the file transfer notice instructs the network deviceto take over download of a file which is requested by the file transferrequest and is in the network device; the transfer unit is to, after thenotification receiving unit receives the file transfer notice, take overexecution of transmission of the file through a data link to transferthe file between the network device and the FTP client.
 13. The networkdevice of claim 12, wherein the transfer unit comprises: a judgmentsub-unit to judge whether the data link to transfer the file existsbetween the network device and the FTP client; an establishment sub-unitto establish the data link to transfer the file between the networkdevice and the FTP client when a judgment result of the judgmentsub-unit is no; a transfer sub-unit to execute transmission of the filethrough the data link used to transfer the file, when the judgmentresult of the judgment sub-unit is yes or when the establishmentsub-unit has established the data link used to transfer the file. 14.The network device of claim 13, wherein the network device furthercomprises a link notification unit; the link notification unit is tosend a data link establishment completion notice to the FTP servermaster process after the establishment sub-unit has established the datalink and before the transfer sub-unit executes transmission of the filethrough the data link established by the establishment sub-unit.
 15. Thenetwork device of claim 13, wherein: the network device furthercomprises a link manage unit to, after the transfer sub-unit completestransmission of the file, close the data link used to transfer the filebetween the network device and the FTP client, and send a file transfercompletion notice to the FTP server master process.